Reactive microgel and photosensitive resin composition containing the reactive microgel for flexographic printing plate

ABSTRACT

A reactive microgel suitable for a photosensitive resin composition for a water-developable flexographic printing plate, which has an average particle diameter to 10 μm, and is formed of 
     microgel particles, as a core, synthesized from an acrylic monomer in an aqueous medium in the presence of an oil-soluble initiator and in the presence of a reactive polymer emulsifier which is an adduct of a neutralized product of an acrylic copolymer having a tertiary amino group with a compound having an epoxy group and an α, β-unsaturated double bond, and a nonionic emulsifier having an HLB of 12 to 16, and 
     a compound having an epoxy group and an α, β-unsaturated double bond, attached to surfaces of the microgel particles.

This application is a division of application Ser. No. 08/386,087, filedFeb. 9, 1995.

FIELD OF THE INVENTION

The present invention relates to a novel reactive microgel and aphotosensitive resin composition for a water-developable flexographicprinting plate. More specifically it relates to a reactive microgelhaving water-developability useful as a raw material for awater-developable flexographic printing plate, and a photosensitiveresin composition containing the reactive microgel and being used for awater-developable flexographic printing plate.

PRIOR ART OF THE INVENTION

In recent years, flexographic printing has been spotlighted with themodernization of packaging. The method of producing a conventionalflexographic printing plate requires at least three steps of thepreparation of printing plate of a metal, the replication and thevulcanization of a rubber, and these steps require technical proficiencyand a long period of time for the production. That is, the conventionalflexographic printing plate has been expensive. For overcoming thisdefect, a solvent-developable printing plate of a photosensitive resinhas been developed so that a flexographic printing plate can be producedin a simple process. For the solvent-developable printing plate,however, it is required to use a halogen-containing solvents such astrichroloethylene or perchroloethylene as a developer solution. Thesolvent-developable printing plate is therefore tends to be limited inuse in view of recent problems of an adverse influence on environmentsand harmfulness to a human body.

On the other hand, studies have been made of halogen-free substitutesolvents as a developer solution. However, these substitute solvents arelimited in use since they are insufficient in development andcombustible.

Further, for a solvent-developable flexographic printing plate, adiene-based rubber material having a high molecular weight is used as araw material in many cases, and the solvent-developable flexographicprinting plate structually has problems in that it is poor in heatresistance, oxidation resistance and ozone resistance. It has beentherefore desired to develop a water-developable flexographic printingplate which is harmless to a human body and is free from causingenvironmental problems.

Under the circumstances, JP-A-60-173055 and JP-A-60-211451 disclosescompositions containing a hydrophobic elastomeric material and ahydrophilic polymer compound. However, these compositions have a defectin that the flexographic printing plates obtained therefrom are poor inwater resistance, since the compositions contain a relatively largeamount of the hydrophilic polymer compound for achieving sufficientdevelopability with water.

On the other hand, JP-A-52-173455 and JP-A-63-8648 disclose aphotosensitive material containing fine particles of a resin or amicrogel, or a composition for a flexographic printing plate. However,it is not sufficient for obtaining developability with water to simplycontain the fine particles of a resin or a microgel. Further, thiscomposition in which the fine particles of a resin are dispersed in amatrix having a high molecular weight is an inherently nonhomogeneoussystem, and a flexographic printing plate made of the composition isnon-transparent due to the refractive index difference of thecomposition. As a result, no sufficient resolution can be accomplished.Further, when attempts are made to use a raw material which does notcause the refractive index difference, it is still difficult to satisfyother properties required of a flexographic printing plate.

Further, JP-A-5-150451 discloses a water-developable photosensitiveresin composition containing three-dimensionally crosslinked fineparticles produced from a conjugated diene monomer, a hydrophobicelastomer having a diene-based unit and a hydrophilic polymer. Thiscomposition shows the rubbery resilience which a flexographic printingplate is required to have, while it is poor in water resistance since ahydrophilic polymer is contained. Further, it is poor in heatresistance, oxidation resistance and ozone resistance since a conjugateddiene-based material is contained, and it is therefore required toincorporate relatively large amounts of an antioxidant and an agent forthe prevention of deterioration with ozone. Moreover, a pressureapparatus is required for obtaining crosslinked fine particles by thepolymerization of the diene-based monomer.

On the other hand, the present inventors have found that the followingresin composition for a water-developable flexographic printing platehas sufficient rubbery resilience and sufficient water resistance, andhave already proposed the same (see JP-A-05-32743). This resincomposition comprises a microgel having core and shell portions bondedto each other and having a hydrophilic group and a reactive group on itssurface, obtained by copolymerizing an acrylic monomer containing atertiary amino group and other acrylic monomer, neutralizing theresultant copolymer with an acid, adding an epoxy group and an α,β-ethylenically unsaturated compound to the neutralized copolymer toprepare a reactive polymer emulsifying agent, polymerizing apolydiene-based acrylate and/or a polyurethane-based acrylate in thepresence of the reactive polymer emulsifying agent, and further addingan epoxy group and an α, β-ethylenically unsaturated compound to thesurface of the resultant resin fine particles, a diene-based polymer anda photosensitive monomer. However, the above resin composition issomewhat poor in heat resistance, oxidation resistance and ozoneresistance due to the diene-based material. Further, there is anotherdefect in that since the polybutadiene-based acrylate and thepolyurethane-based acrylate are expensive, the flexographic printingplate is expensive.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel reactivemicrogel which can be suitably applied to a photosensitive resincomposition for a water-developable flexographic printing plate.

It is another object of the present invention to provide a novelreactive microgel which can be stably synthesized with a simpleapparatus and can be suitably applied to a photosensitive resincomposition for a water-developable flexographic printing plate.

It is further another object of the present invention to provide aphotosensitive resin composition for a water-developable flexographicprinting plate which has rubbery resilience and is excellent in waterresistance, oxidation resistance and ozone resistance.

According to the present invention, there is provided a reactivemicrogel having an average particle diameter of 1 to 10 μm, formed of

microgel particles, as a core, synthesized from an acrylic monomer in anaqueous medium in the presence of an oil-soluble initiator and in thepresence of a reactive polymer emulsifier which is an adduct of aneutralized product of an acrylic copolymer having a tertiary aminogroup with a compound having an epoxy group and an α,β-unsaturateddouble bond, and a nonionic emulsifier having an HLB of 12 to 16, and

a compound having an epoxy group and an unsaturated double bond,attached surfaces of the microgel particles.

According to the present invention, there is further provided aphotosensitive resin composition for water-developable flexographicprinting plate, comprising 30 to 80 parts by weight of the abovereactive microgel (A), 5 to 60 parts by weight of an ethylene-vinylacetate copolymer and/or an ethylene-ethyl acrylate copolymer (B), 1 to60 parts by weight of a compound having an α, β-ethylenicallyunsaturated double bond (C) and 0.01 to 10 parts by weight of aphotopolymerization initiator (D).

DETAILED DESCRIPTION OF THE INVENTION

The reactive microgel of the present invention will be explainedhereinafter. The reactive microgel of the present invention has anaverage particle diameter of 1 to 10 μm, and is formed of

microgel particles, as a core, synthesized from an acrylic monomer in anaqueous medium in the presence of an oil-soluble initiator and in thepresence of a reactive polymer emulsifier which is an adduct of aneutralized product of an acrylic copolymer having a tertiary aminogroup with a compound having an epoxy group and an α, β-unsaturateddouble bond, and a nonionic emulsifier having an HLB of 12 to 16, and

a compound having an epoxy group and unsaturated double bond attached tosurfaces of the microgel particles.

The acrylic copolymer having a tertiary amino group is obtained bycopolymerizing a monomer having a tertiary amino group such asN,N-dimethylaminoethyl (meth)acrylate or N,N-diethylaminoethyl(meth)acrylate and other acrylic monomer. The "other" acrylic monomerincludes C₁ -C₂₂ alkyl (meth)acrylates such as methyl (meth)acrylate,ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate and stearyl(meth)acrylate and (meth)acrylates having a hydroxyl group such as2-hydroxy (meth)acrylate and hydroxypropyl (meth)acrylate.

The acrylic copolymer having a tertiary amino group preferably has aglass transition temperature (to be referred to as "Tg" hereinafter) of20° C. or lower to impart the flexographic printing plate with rubberyresilience and flexibility. Further, the content of a component from themonomer having a tertiary amino group in the copolymer is preferably 10to 50 % by weight. When the above content is less than 10% by weight,the polymer emulsifier has insufficient hydrophilic nature, and showsinsufficient emulsification performance. When the above content exceeds50% by weight, the flexographic printing plate shows poor waterresistance.

The acrylic copolymer having a tertiary amino group is neutralized withan acid such as hydrochloric acid, formic acid, acetic acid,(meth)acrylic acid or succinic acid, and then a compound having an epoxygroup and an α, β-unsaturated double bond is attached thereto, so thatthe reactive polymer emulsifier is obtained. The compound having anepoxy group and an α, β-unsaturated double bond includes glycidylacrylate and glycidyl methacrylate.

The nonionic emulsifier having an HLB of 12 to 16 is selected frompolyoxyethylene lauryl available, for example, in the trade of Emulgen108 or 120, polyoxyethylene cetyl ether available, for example, in thetrade name of Emulgen 220, polyoxyethylene stearyl alcohol available,for example, in the trade name of Emulgen 320P, polyoxyethylene oleylether available, for example, in the trade name of Emulgen 409P or 420,polyoxyethylene octylphenyl ether available, for example, in the tradename of Emulgen 810, polyoxyethylene nonylphenyl ether available, forexample, in the trade name of Emulgene 910 or 911, polyoxyethylenesorbitane monolaurate available, for example, in the trade name ofRHEODOL TW-S120, polyoxyethylene sorbitol tetraoleate available, forexample, in the trade name of RHEODOL 450, polyethylene glycolmonolaurate available, for example, in the trade name of EMANON 1112(Emulgen and EMANON are all trade names of Kao Corp.) and a reactivenonionic emulsifier having an acryloyl group available, for example, inthe trade name of Adecalia soap NE-10 (supplied by Asahi Denka K. K.).

The oil-soluble initiator includes 2,2'-azobis(2-methylbutyronitrile),2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile) and2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).

The acrylic monomer to form a core includes C₁ -C₂₂ alkyl(meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate,butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,lauryl (meth)acrylate and stearyl (meth)acrylate and (meth)acrylateshaving a hydroxyl group such as 2-hydroxy (meth)acrylate andhydroxypropyl (meth)acrylate.

The above reactive polymer emulsifier, the above nonionic emulsifierhaving an HLB of 12 to 16, the above oil-soluble initiator and the aboveacrylic monomer to form a core are uniformly mixed, and either themixture is stirred with a disper, a homomixer or the like in thepresence of an aqueous medium, or an aqueous medium is added dropwise tothe mixture while the mixture is stirred, to prepare a monomer mixturein the form of oil drops. Then, the monomer mixture is polymerized underheat under nitrogen gas current, whereby an aqueous dispersion of amicrogel is obtained. The microgel preferably has a Tg of 20° C. orlower to obtain a flexographic printing plate having rubbery resilienceand flexibility.

The amount of the reactive polymer emulsifier per 100 parts by weight ofthe acrylic monomer to form a core is 1 to 20 parts by weight,preferably 2 to 15 parts by weight. The amount of the nonionicemulsifier per 100 parts by weight of the acrylic monomer to form a coreis 0.1 to 15 parts by weight, preferably 0.5 to 10 parts by weight. Whenthe amount of any one of the above emulsifiers is smaller than the lowerlimit of the above corresponding amount range, the stability of theemulsion is poor, or it is difficult to impart the microgel particlesurface with sufficient hydrophilic nature. When the above amount is toolarge, the flexographic printing plate may show poor water resistance.

The amount of the oil-soluble initiator per 100 parts by weight of theacrylic monomer to form a core is preferably 0.1 to 5 parts by weight.When the amount of the oil-soluble initiator is too small, thepolymerization rate does not increase as required, and the acrylicmonomer may remain. When it is too large, the molecular weight of themicrogel does not increase as required, and the flexographic printingplate may be poor in durability and flexibility.

The microgel is obtained as there-dimensionally crosslinked resin fineparticles when it is synthesized from the above acrylic monomer alone.However, for imparting a flexographic printing plate with rubberyresilience, durability and stability of developability with time (i.e.,for increasing the crosslinking degree of the core), it is preferred touse a polyfunctional acrylic monomer in combination. The polyfunctionalacrylic monomer is selected from di(meth)acrylates such as ethyleneglycol di(meth)acrylate, hexamethylenediol di(meth)acrylate, neopentylglycol di(meth)acrylate and C₁₄ -C₁₅ alkylene di(meth)acrylate,trimethylolpropane triacrylate, pentaerythritol tetraacrylate andglycerin triacrylate.

The amount of the above poly functional acrylic monomer based on theacrylic monomer to form a core is preferably 1 to 40% by weight. Whenthe amount of the polyfunctional acrylic monomer is less than the abovelower limit, the flexographic printing plate is liable to be poor inwater resistance and stability of developability with time. When it isgreater than the above upper limit, the microgel is liable to have toohigh a hardness to give a flexographic printing plate having a lowhardness and flexibility.

A compound having an epoxy group and an α, β-unsaturated double bond isadded to the aqueous dispersion of the microgel obtained above, and themixture is heated, whereby an aqueous dispersion of the reactivemicrogel of the present invention is obtained. The compound having anepoxy group and an α, β-unsaturated double bond includes glycidylacrylate and glycidyl methacrylate. The so-obtained aqueous dispersionof the reactive microgel is dried under heat and/or under reducedpressure, whereby a microgel powder or microgel flakes are obtained.

The average particle diameter of the reactive microgel obtained above ispreferably 1 to 10 μm, more preferably 2 to 5 μm, and the reactivemicrogel having such an average particle diameter can be used in thephotosensitive resin composition for a flexographic printing plate,provided by the present invention. When the average particle diameter ofthe reactive microgel is smaller than the above lower limit, theflexographic printing plate is poor in water-developability andstability of water-developability with time. When the above averageparticle diameter is larger than the above upper limit, the resolutionof the flexographic printing plate is adversely affected. The reactivemicrogel generally has a refractive index of 1.46 to 1.49.

The photosensitive resin composition for a water-developableflexographic printing plate, provided by the present invention, will beexplained hereinafter.

The photosensitive resin composition of the present invention contains30 to 80 parts by weight of the above reactive microgel (A) of thepresent invention, 5 to 60 parts by weight of an ethylene-vinyl acetatecopolymer and/or an ethylene-ethyl acrylate copolymer (B), 1 to 60 partsby weight of a compound having an α, β-ethylenically unsaturated doublebond (C) and 0.01 to 10 parts by weight of a photopolymerizationinitiator (D).

When the amount of the tertiary amino group (A) is small let than theabove lower limit, the flexographic printing plate is liable to show nowater-developability. When it is larger than the above upper limit, theflexographic printing plate is liable to be poor in strength and waterresistance.

When the amount of the ethylene-vinyl acetate copolymer and/or theethylene-ethyl acrylate copolymer (B) is smaller than the above lowerlimit, the flexographic printing plate is liable to tie unsatisfactoryin strength and water resistance. When it is larger than the above upperlimit, the flexographic printing plate is liable to be poor inwater-developability.

When the amount of the compound having an α, β-ethylenically unsaturateddouble bond (C) is smaller than the above lower limit, the flexographicprinting plate is liable to be unsatisfactory in water resistance andphysical properties. When it is greater than the above upper limit, theprinting plate has too high a rubber hardness to be used as aflexographic printing plate.

The ethylene-vinyl acetate copolymer and the ethylene-ethyl acrylatecopolymer (B) can be obtained by copolymerizing ethylene and vinylacetate or ethyl acrylate in any amounts, while the ethylene-vinylacetate copolymer and the ethylene-ethyl acrylate copolymer (B)preferably have a refractive index different from that of the reactivemicrogel of the present invention by 0.02 or less, and a JIS-A hardnessof 60 or less. When the refractive index of the ethylene-vinyl acetatecopolymer and/or the ethylene-ethyl acrylate copolymer (B) is differentfrom that of the reactive microgel (A) by more than 0.2, thephotosensitive resin composition is free of transparency, and theresolution required of a flexographic printing plate cannot be obtained.When the above JIS-A hardness exceeds 60, the photosensitive resincomposition has a high hardness, and the use thereof for a flexographicprinting plate is limited.

The compound having an α, β-ethylenically unsaturated double bond (C)serves to impart the photosensitive resin composition withphoto-curability. The photosensitive resin composition containing thecompound having an α, β-ethylenically unsaturated double bond incombination with the photopolymerization initiator cures itself afterexposed to light, and gives a resolution required as a flexographicprinting plate when developed with water. The compound having an α,β-ethylenically unsaturated double bond (C) is not specially limited ifit is compatible with the ethylene-vinyl acetate copolymer and theethylene-ethyl acrylate copolymer (B) before and after thephotosensitive resin composition is cured, or if it has almost nodifferent refractive index from that of the above copolymer(s) (B).

The compound having an α, β-ethylenically unsaturated double bond (C) isselected from monofunctional monomers and polyfunctional monomers. Themonofunctional monomers include C₁ -C₂₂ alkyl (meth)acrylates such asmethyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate andstearyl (meth)acrylate, (meth)acrylates having a hydroxyl group such as2-hydroxy (meth)acrylate and hydroxypropyl (meth)acrylate, norbornyl(meth)acrylate, vinylpyrrolidone, vinylaniline and acrylamide.

The polyfunctional monomers include ethylene glycol di(meth)acrylate,hexamethylenediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,C₁₄ -C₁₅ alkylene di(meth)acrylate, trimethylolpropane triacrylate,pentaerythritol tetraacrylate and glycerin triacrylate, polyesteracrylate, polyurethane acrylate and polyol acrylate.

The polyfunctional monomer is preferred since it is excellent inphoto-curability. The above polyfunctional monomers may be used alone orin combination. Further, the polyfunctional monomer may be used incombination with the monofunctional monomer.

The photopolymerization initiator (D) is not specially limited if itreacts when exposed to ultraviolet light or the like and cures the abovemonomers. The photopolymerization initiator (D) includes benzoin ethers,benzophenones, xanthones and acetophenones. These initiators may be usedalone or in combination. Further, the photopolymerization initiator (D)may be used in combination with a photo-initiator auxiliary selectedfrom amines.

The photosensitive resin composition for a water-developableflexographic printing plate, provided by the present invention, mayfurther contain an organic or inorganic filler, a heat polymerizationinhibitor, an antioxidant, a preventer for deterioration with ozone, adye and a flow regulator.

The photosensitive resin composition of the present invention is kneadedwith a kneading apparatus such as a two-roll mill, a Banbury mixer, akneader or an extruder, and formed into a laminate of a substrate film,the photosensitive resin composition and a cover film to obtain awater-developable flexographic printing plate. The so-obtainedwater-developable flexographic printing plate is exposed to lightthrough the substrate film, the cover film is removed, and a negativefilm is intimately attached. The resultant printing plate is exposed tolight in an appropriate dose, developed by brush-washing an unexposedportion with water or hot water, dried and post-exposed to obtain aflexographic printing plate.

EXAMPLES

The present invention will be detailed hereinafter with reference toExamples, in which "part" stands for "part by weight".

Example 1

A two-liter flask was charged with 195 parts of N,N-dimethylaminoethylmethacrylate, 455 parts of n-lauryl methacrylate and 350 parts ofisopropanol, and while the mixture was stirred under nitrogen current,the mixture was temperature-increased to 75° C. Then, 6.5 parts ofazobisisobutyronitrile was added, and the mixture was heated at 80° C.for 5 hours to give a polymer solution. The polymer solution was allowedto stand overnight at room temperature, and 75 parts of acetic acid and50 parts of glycidyl methacrylate were added. While the mixture wasstirred under air current, the mixture was heated at 50° C. for 5 hoursto give a reactive polymer emulsifier solution.

A two-liter flask was charged with 50 parts of the above-obtainedreactive polymer emulsifier, 15 parts of a nonionic emulsifier ("Emulgen420", HLB 13.6, supplied by Kao Corp.), 270 parts of 2-ethylhexylacrylate, 30 parts of hexamethylene glycol diacrylate and 2 parts ofazobisisobutyronitrile, and while the mixture was moderately stirred atroom temperature, 600 parts of ion-exchanged water was dropwise addedover 1 hour. Then, under nitrogen current, the mixture wastemperature-increased to 80° C. and maintained at this temperature for 3hours to give an aqueous dispersion of a microgel. The aqueousdispersion of a microgel was allowed to stand overnight at roomtemperature, and then 20 parts of glycidyl methacrylate was added. Themixture was heated at 50° C. for 3 hours to give an aqueous dispersionof a reactive microgel. The aqueous dispersion of a reactive microgelwas measured for an average particle diameter by a light scatteringmethod to show 3 μm. The aqueous dispersion also showed a refractiveindex of 1.47. The aqueous dispersion of a reactive microgel wasfreeze-dried to give a white powder.

60 Parts of the above-obtained reactive microgel powder, 30 parts of anethylene-vinyl acetate copolymer ("Evaflex EV40X", JIS-A hardness 43,refractive index 1.48, supplied by Du Pont-Mitsui Polychemicals Co.,Ltd. ), 10 parts of hexamethylene glycol diacrylate, 0.5 part of aphotopolymerization initiator ("Darocure 1173", supplied by Merck) and0.1 part of hydroquinone were kneaded with a double-armed kneader atroom temperature for 20 minutes. Then, the resultant composition wassandwiched with polyester films and pressed to give a raw flexographicprinting plate having a thickness of 1.5 min. One surface of the rawflexographic printing plate was exposed to a 15 W ultraviolet light lampfor 10 seconds, and then, the polyester film forming the other surfacewas removed. A negative film was intimately attached to the revealedsurface, and the surface was exposed to the 15 W ultraviolet light lampfor 3 minutes. The raw flexographic printing plate was developed bybrush-washing it with water for 10 minutes, dried at 60° C. for 15minutes, and post-exposed to the 15 W ultraviolet light lamp for 10minutes to give a flexographic printing plate. The so-obtainedflexographic printing plate had a JIS-A hardness of 50, and it showed athickness change of 1.8% after tested for water resistance by immersingit in ion-exchanged water for 1 day. Concerning the transparency, theraw flexographic printing plate had a haze value of 30, and the curedflexographic printing plate had a haze value of 35. The raw flexographic printing plate showed almost no change in water-developabilityafter allowed to stand at 50° C. for 2 months and after allowed to standat 120° C. for 2 hours.

Example 2

50 Parts of the same reactive microgel powder as that obtained inExample 1, 30 parts of an ethylene-vinyl acetate copolymer ("EvaflexEV45LX", JIS-A hardness 34, refractive index 1.47, supplied by DuPont-Mitsui Polychemicals Co., Ltd.), 15 parts of C₁₄ -C₁₅ alkyldiacrylate ("SR2000A", supplied by Kayaku Sartomer K. K.) and 0.1 partof a photopolymerization initiator ("Irgacure 651", supplied by CibaGeigy) were kneaded with a two-roll mill for 10 minutes. Then, theresultant composition was processed in the same manner as in Example 1to give a raw flexographic printing plate having a thickness of 1.5 mm.The raw flexographic printing plate was exposed, developed andpost-exposed in the same manner as in Example 1 to give a flexographicprinting plate. The so-obtained flexographic printing plate had a JIS-Ahardness of 45, and it showed a thickness change of 1.9% after testedfor water resistance by immersing it in ion-exchanged water for 1 day.Concerning the transparency, the raw flexographic printing plate had ahaze value of 36, and the cured flexographic printing plate had a hazevalue of 40. The raw flexographic printing plate showed almost no changein water-developability after allowed to stand at 50° C. for 2 months,and after allowed to stand at 120° C. for 2 hours.

Example 3

50 Parts of the same reactive microgel powder as that obtained inExample 1, 35 parts of an ethylene-ethyl acrylate copolymer ("EvaflexEEA A-709", JIS-A hardness 49, refractive index 1.47, supplied by DuPont-Mitsui Polychemicals Co., Ltd.), 15 parts of C₁₄ -C₁₅ alkyldiacrylate ("SR2000A", supplied by Kayaku Sartomer K. K.) and 0.1 partof a photopolymerization initiator ("Irgacure 651", supplied by CibaGeigy) were kneaded with a two-roll mill for 10 minutes. Then, theresultant composition was processed in the same manner as in Example 1to give a raw flexographic printing plate having a thickness of 1.5 mm.The raw flexographic printing plate was exposed, developed andpost-exposed in the same manner as in Example 1 to give a flexographicprinting plate. The so-obtained flexographic printing plate had a JIS-Ahardness of 48, and it showed a thickness change of 1.7% after testedfor water resistance by immersing it in ion-exchanged water for 1 day.Concerning the transparency, the raw flexographic printing plate had ahaze value of 34, and the cured flexographic printing plate had a hazevalue of 30. The raw flexographic printing plate showed almost no changein water-developability after allowed to stand at 50° C. for 2 months,and after allowed to stand at 120° C. for 2 hours.

Example 4

A two-liter flask was charged with 195 parts of N,N-diethylaminoethylmethacrylate, 455 parts of 2-ethylhexyl methacrylate and 350 parts ofisopropanol, and while the mixture was stirred under nitrogen current,the mixture was temperature-increased to 75° C. Then, 6.5 parts ofazobisisobutyronitrile was added, and the mixture was heated at 80° C.for 5 hours to give a polymer solution. The polymer solution was allowedto stand overnight at room temperature, and 60 parts of acetic acid and50 parts of glycidyl methacrylate were added. While the mixture wasstirred under air current, the mixture was heated at 50° C. for 5 hoursto give a reactive polymer emulsifier solution.

A two-liter flask was charged with 50 parts of the above-obtainedreactive polymer emulsifier, 10 parts of a nonionic emulsifier ("Emulgen120", HLB 15.3, supplied by Kao Corp.), 270 parts of 2-ethylhexylacrylate, 40 parts of C₁₄ -C₁₅ alkyl diacrylate and 2 parts ofazobisisobutyronitrile, and while the mixture was moderately stirred atroom temperature, 600 parts of ion-exchanged water was dropwise addedover 1 hour. Then, under nitrogen current, the mixture wastemperature-increased to 65° C. and maintained at this temperature for 3hours to give an aqueous dispersion of a microgel. The aqueousdispersion of a microgel was allowed to stand overnight at roomtemperature, and then 20 parts of glycidyl methacrylate was added. Themixture was heated at 50° C. for 3 hours to give an aqueous dispersionof a reactive microgel. The aqueous dispersion of a reactive microgelwas measured for an average particle diameter by a light scatteringmethod to show 3 μm. The aqueous dispersion also showed a refractiveindex of 1.47. The aqueous dispersion of a reactive microgel wasfreeze-dried to give a white powder.

50 Parts of the above-obtained reactive microgel powder, 40 parts of anethylene-vinyl acetate copolymer ("Evaflex EV40X", JIS-A hardness 43,refractive index 1.48, supplied by Du Pont-Mitsui Polychemicals Co.,Ltd.), 5 parts of dipentaerythritol hexaacrylate, 5 parts of isophoroneacrylate, 0.5 part of a photopolymerization initiator ("Darocure 1173",supplied by Merck) and 0.1 part of hydroquinone were kneaded with atwin-screw kneader at 100° C. for 5 minutes. Then, the resultantcomposition was processed i n the same manner as in Example 1 to give araw flexographic printing plate having a thickness of 1.5 mm. The rawflexographic printing plate was exposed, developed and post-exposed inthe same manner as in Example 1 to give a flexographic printing plate.The so-obtained flexographic printing plate had a JIS-A hardness of 45,and it showed a thickness change of 2.0% after tested for waterresistance by immersing it in ion-exchanged water for 1 day. Concerningthe transparency, the raw flexographic printing plate had a haze valueof 35, and the cured flexographic printing plate had a haze value of 35.The raw flexographic printing plate showed almost no change inwater-developability after allowed to stand at 50° C. for 2 months, andafter allowed to stand at 120° C. for 2 hours.

Example 5

60 Parts of the same reactive microgel powder as that obtained inExample 1, 30 parts of an ethylene-vinyl acetate copolymer ("EvaflexEV450", JIS-A hardness 90, refractive index 1.49, supplied by DuPont-Mitsui Polychemicals Co., Ltd.), 10 parts of hexamethylene glycoldiacrylate, 0.5 part of a photopolymerization initiator ("Datacure1173", supplied by Merck) and 0.1 part of hydroquinone were kneaded witha double-armed kneader at room temperature for 20 minutes. Then, theresultant composition was processed in the same manner as in Example 1to give a raw flexographic printing plate having a thickness of 1.5 mm.The raw flexographic printing plate was exposed, developed andpost-exposed in the same manner as in Example 1 to give a flexographicprinting plate. The so-obtained flexographic printing plate had a JIS-Ahardness of 75, and it showed a thickness change of 1.7% after testedfor water resistance by immersing it in ion-exchanged water for 1 day.Concerning the transparency, the raw flexographic printing plate had ahaze value of 60, and the cured flexographic printing plate had a hazevalue of 57. The raw flexographic printing plate showed almost no changein water-developability after allowed to stand at 50° C. for 2 months,and after allowed to stand at 120° C. for 2 hours.

Comparative Example 1

A 2-liter flask was charged with 15 parts of a nonionic emulsifier("Emulgen 420", HLB 13.6), 270 parts of 2-ethylhexyl acrylate, 30 partsof hexamethylene glycol diacrylate and 2 parts ofazobisisobutyronitrile, and while the mixture was stirred at roomtemperature, 600 parts of ion-exchanged water was dropwise added over 1hour. Then, the mixture was temperature-increased to 80° C. undernitrogen current to carry out the polymerization, while thepolymerization was not carried out stably and the mixture was gelled.

Comparative Example 2

A two-liter flask was charged with 50 parts of the same reactive polymeremulsifier as that obtained in Example 1, 15 parts of a nonionicemulsifier ("Emulgen 950", HLB 18.2, supplied by Kao Corp.), 270 partsof 2-ethylhexyl acrylate, 30 parts of hexamethylene glycol diacrylateand 2 parts of azobisisobutyronitrile, and while the mixture wasmoderately stirred at room temperature, 600 parts of ion-exchanged waterwas dropwise added over 1 hour. Then, the mixture wastemperature-increased to 80° C. under nitrogen current to carry out thepolymerization, while the polymerization was not carried out stably andthe mixture was gelled.

Comparative Example 3

A two-liter flask was charged with 270 parts of 2-ethylhexyl acrylate,30 parts of hexamethylene glycol diacrylate, 10 parts of sodiumdodecylbenzenesulfonate, 15 parts of a nonionic emulsifier ("Emulgen420", HLB 13.6, supplied by Kao Corp.) and 600 parts of ion-exchangedwater, and while the mixture was stirred, the mixture wastemperature-increased to 65° C. under nitrogen current. Further, 20parts of a 5% ammonium persulfate aqueous solution and 20 parts of a 5%sodium thiosulfate aqueous solution both of which were water-solublepolymerization initiators were added, and the mixture was heated at 70°C. for 5 hours to give an aqueous dispersion of a microgel having anaverage particle diameter, measured by a light scattering method, of 0.2μm and a refractive index of 1.47. The so-obtained aqueous dispersion ofa microgel was free-dried to give a white powder.

60 Parts of the above-obtained reactive microgel powder, 30 parts of anethylene-vinyl acetate copolymer ("Evaflex EV40X", JIS-A hardness 43,refractive index 1.48, supplied by Du Pont-Mitsui Polychemicals Co.,Ltd.), 10 parts of hexamethylene glycol diacrylate, 0.5 part of aphotopolymerization initiator ("Darocure 1173", supplied by Merck) and0.1 part of hydroquinone were kneaded with a double-armed kneader atroom temperature for 20 minutes. Then, the kneaded mixture was processedin the same manner as in Example 1 to give a raw flexographic printingplate having a thickness of 1.5 mm. This raw flexographic printing plateshowed no developability with water at 50° C. when it was in anon-exposed state.

Comparative Example 4

A two-liter flask was charged with 130 parts of methacrylic acid, 520parts of n-lauryl methacrylate and 350 parts of isopropanol, and themixture was temperature-increased to 75° C. with stirring under nitrogencurrent. Then, 6.5 parts of azobisisobutyronitrile was added, and themixture was heated at 80° C. for 5 hours to give a polymer solution.This polymer solution was allowed to stand overnight at roomtemperature, and 600 parts of a 10% sodium hydroxide aqueous solutionwas added to give a polymer emulsifier solution.

A two-liter flask was charged with 80 parts of the above-obtainedpolymer emulsifier, 15 parts of a nonionic emulsifier ("Emulgen 420",HLB 13.6, supplied by Kao Corp.), 270 parts of 2-ethylhexyl acrylate, 30parts of hexamethylene glycol diacrylate and 2 parts ofazobisisobutyronitrile, and while the mixture was moderately stirredunder nitrogen current, 600 parts of ion-exchanged water was added over1 hour. Then, under nitrogen current, the mixture wastemperature-increased to 80° C. and this temperature was maintained for3 hours to give an aqueous dispersion of a microgel. The aqueousdispersion of a reactive microgel was measured for an average particlediameter by a light scattering method to show 3 μm. The aqueousdispersion also showed a refractive index of 1.47. The aqueousdispersion of a reactive microgel was freeze-dried to give a whitepowder.

50 Parts of the above-obtained microgel powder, 30 parts of anethylene-vinyl acetate copolymer ("Evaflex EV40X", JIS-A hardness 43,refractive index 1.48, supplied by Du Pont-Mitsui Polychemicals Co.,Ltd.), 10 parts of hexamethylene glycol diacrylate, 0.5 part of aphotopolymerization initiator ("Darocure 1173", supplied by Merck) and0.1 part of hydroquinone were kneaded with a double-armed kneader atroom temperature for 20 minutes. Then, the resultant composition wasprocessed in the same manner as in Example 1 to give a raw flexographicprinting plate having a thickness of 1.5 mm. The raw flexographicprinting plate was exposed, developed and post-exposed in the samemanner as in Example 1 to give a flexographic printing plate. Theso-obtained flexographic printing plate had a JIS-A hardness of 50,while it showed a thickness change of 8.0% after tested for waterresistance by immersing it in ion-exchanged water for 1 day. Theimmersed flexographic printing plate was considerably fragile.

Comparative Example 5

A two-liter flask was charged with 50 parts of the same reactive polymeremulsifier as that obtained in Example 1, 15 parts of a nonionicemulsifier ("Emulgen 420", HLB 13.6, supplied by Kao Corp.), 270 partsof 2-ethylhexyl acrylate, 30 parts of hexamethylene glycol diacrylateand 2 parts of azobisisobutyronitrile, and while the mixture wasvigorously stirred at room temperature, 600 parts of ion-exchanged waterwas dropwise added over 1 hour. Then, the mixture was stirred with ahomomixer for 60 minutes. Under nitrogen current, the mixture wastemperature-increased to 80° V, and this temperature was maintained for3 hours to give an aqueous dispersion of a microgel. The so-obtainedaqueous dispersion of a microgel was allowed to stand overnight at roomtemperature. Then, 20 parts of glycidyl methacrylate was added, and themixture was heated at 50° C. for 3 hours to give an aqueous dispersionof a reactive microgel. The aqueous dispersion of a reactive microgelwas measured for an average particle diameter by a light scatteringmethod to show 0.4 μm. The aqueous dispersion also showed a refractiveindex of 1.47. The aqueous dispersion of a reactive microgel wasfreeze-dried to give a white powder.

60 Parts of the above-obtained reactive microgel powder, 30 parts of anethylene-vinyl acetate copolymer ("Evaflex EV40X", JIS-A hardness 43,refractive index 1.48, supplied by Du Pont-Mitsui Polychemicals Co.,Ltd.), 10 parts of hexamethylene glycol diacrylate, 0.5 part of aphotopolymerization initiator ("Darocure 1173", supplied by Merck) and0.1 part of hydroquinone were kneaded with a double-armed kneader atroom temperature for 20 minutes. Then, the resultant composition wasprocessed in the same manner as in Example 1 to give a raw flexographicprinting plate having a thickness of 1.5 mm. The raw flexographicprinting plate was exposed, developed and post-exposed in the samemanner as in Example 1 to give a flexographic printing plate. Theso-obtained flexographic printing plate had a JIS-A hardness of 50, andit showed a thickness change of 1.8% after tested for water resistanceby immersing it in ion-exchanged water for 1 day. Concerning thetransparency, the raw flexographic printing plate had a haze value of30, and the cured flexographic printing plate had a haze value of 35.However, the raw flexographic printing plate showed no developabilitywith water after allowed to stand at 50° C. for 3 days.

Comparative Example 6

50 Parts of the same reactive microgel powder as that obtained inExample 1, 35 parts of an ethylenepropylene rubber ("JSREP11",refractive index 1.47, supplied by Japan Synthetic Rubber), 15 parts ofC₁₄ -C₁₅ alkyl diacrylate ("SR2000A", supplied by Kayaku Sartomer K. K.)and 0.1 part of a photopolymerization initiator ("Irgacure 651",supplied by Ciba Geigy) were kneaded with a two-roll mill for 10minutes. Then, the resultant composition was processed in the samemanner as in Example 1 to give a raw flexographic printing plate havinga thickness of 1.5 mm. This raw flexographic printing plate had a hazevalue of 30 or had excellent transparency. However, when theflexographic printing plate was exposed to a 15 W ultraviolet light lampfor 20 minutes, it was free of flexibility and not suitable for the usethereof as a flexographic printing plate.

Comparative Example 7

50 Parts of the same reactive microgel powder as that obtained inExample 1, 35 parts of an acrylic rubber ("AR72HF", refractive index1.47, supplied by Nippon Zeon Co., Ltd.), 15 parts of C₁₄ -C₁₅ alkyldiacrylate ("SR2000A", supplied by Kayaku Sartomer K. K.) and 0.1 partof a photopolymerization initiator ("Irgacure 551", supplied by CibaGeigy) were kneaded with a two-roll mill for 10 minutes. Then, theresultant composition was processed in the same manner as in Example 1to give a raw flexographic printing plate having a thickness of 1.5 mm.This raw flexographic printing plate had a haze value of 30 or hadexcellent transparency. However, when the flexographic printing platewas cured by exposing it to a 15 W ultraviolet light lamp for 20 minutesand immersed in water for 25 hours, it showed a thickness change of over8%, and was not suitable for the use thereof as a flexographic printingplate.

Comparative Example 8

50 Parts of the same reactive microgel powder as that obtained inExample 1, 35 parts of a butadiene rubber ("JSRBR02LL", refractive index1.51, supplied by Japan Synthetic Rubber), 15 parts of C₁₄ -C₁₅ alkyldiacrylate ("SR2000A", supplied by Kayaku Sartomer K. K.) and 0.1 partof a photopolymerization initiator ("Irgacure 651", supplied by CibaGeigy) were kneaded with a two-roll mill for 10 minutes. Then, theresultant composition was processed in the same manner as in Example 1to give a raw flexographic printing plate having a thickness of 1.5 mm.This raw flexographic printing plate had a haze value of 96 or had notransparency, and no resolution was achieved.

As explained above, according to the present invention, a resincomposition for a water- or hot water-developable photosensitiveflexographic printing plate excellent in water resistance, flexibility,heat resistance, oxidation resistance and ozone resistance and areactive microgel suitable for use therefor can be produced stably at alow cost.

What is claimed is:
 1. A photosensitive resin composition for awater-developable flexographic printing plate, comprising30 to 80 partsby weight of a reactive microgel (A) having an average particle diameterof 1 to 10 μm, formed of microgel particles, as a core, synthesized froman acrylic monomer in an aqueous medium in the presence of anoil-soluble initiator and in the presence of a reactive polymeremulsifier which is an adduct of a neutralized product of an acryliccopolymer having a tertiary amino group with a compound having an epoxygroup and an α,β-unsaturated double bond, and a nonionic emulsifierhaving an HLB of 12 to 16, and a compound having an epoxy group and anα,β-unsaturated double bond, attached to surfaces of the microgelparticles, 5 to 60 parts by weight of an ethylene-vinyl acetatecopolymer and/or an ethylene-ethyl acrylate copolymer (B), 1 to 60 partsby weight of a compound having an α,β-ethylenically unsaturated doublebond (C), and 0.01 to 10 parts by weight of a photopolymerizationinitiator (D).
 2. A composition according to claim 1, wherein theethylene-vinyl acetate copolymer and/or the ethylene-ethyl acrylatecopolymer (B) have/has a refractive index different from a refractiveindex of the reactive microgel (A) by 0.02 or less.
 3. A compositionaccording to claim 1, wherein the ethylene-vinyl acetate copolymerand/or the ethylene-ethyl acrylate copolymer (B) have/has a JIS-Ahardness of 60 or less.
 4. A composition according to claim 1, whereinthe compound having an α, β-ethylenically unsaturated double bond (C) isat least one selected from the group consisting of monofunctionalmonomers and polyfunctional monomers.